The invention disclosed herein pertains to computed X-ray tomography equipment. In particular, the invention comprises apparatus for controlling and protecting the cables that communicate between rotating and stationary parts such as between a gantry structure and the X-ray tube, X-ray detector and other components on the rotating X-ray scanner.
Typical computed tomography apparatus comprises a scanner base, basically a ring having a central opening, mounted for rotation about a generally horizontal axis on an upright member. The body being examined extends axially through the central opening and is supported on a cantilevered X-ray transmissive table top coincident with the axis of rotation. An X-ray source and its associated beam collimator are mounted on the scanner base on one side of the rotational axis and a multicell X-ray detector and its associated data acquisition device are mounted on the base on the other side of the axis. The X-ray beam is collimated into a thin fan-shaped configuration for scanning a thin layer of the body. The X-ray source is usually energized for about 360.degree. of scanner rotation in either direction. The X-ray detector yields signals representative of X-ray attenuation along discrete bundles of rays in the beam. The signals are ultimately converted to digital data which is used by a computer to reconstruct an image of the cross-section or layer of the body that has been scanned as is well known.
A large number of electrical connections must be made between stationary parts of the tomography apparatus and the rotatable scanner base. For example, high voltage cables run to the anode and cathode of the rotating anode X-ray tube. A cable run to the anode rotating motor. Another cable supplies the servo motors that operate the X-ray beam collimator blades. Various cables run to position sensors. There are cables for conducting the multiplexed data from the X-ray detector and its data acquisition system to the computer.
It is desirable to avoid having the cables become tangled, or bent too sharply or overstressed in tension as they go around with the scanner base which may rotate nearly two full revolutions or 720.degree. in each direction to execute a 360.degree. scan of successive layers of the body. Cable tangling or disorderliness could result in the cables being effectively shortened in which case they might break when the power-driven scanner base approaches its rotational limits. Keeping the cables organized in a determinable way and free of undue stresses can be especially problematical where, as in the tomography apparatus to be described later, the scanner base makes about two revolutions for each body layer scanned. Even though the X-ray source is energized for only 360.degree. or, by way of example, two seconds of rotation, the scanner base must rotate from a rest position through about 180.degree. to allow acceleration up to a uniform speed before the X-ray beam is turned on for 360.degree. of rotation. Then the scanner base must decelerate and come to a smooth stop so considerable angular overtravel must be permitted up to a limit. Excessive overtravel must also be avoided and measures must be taken to assure that the scanner base is positively stopped when the permissible rotational limit, that is determined by the length of the cables, is reached.
In some computed tomography equipment slip rings and brushes are used to provide electrically conductive paths between the rotating scanner electrical components and stationary components. This obviates some of the problems that arise with cables but it creates other problems such as the need for insulation for withstanding the high X-ray tube voltages, introduction of noise in the data channels and distortion and wear of the slip rings and their cooperating contacts.